Discovery of testes microbiome gives clues on infertility

Bacteria present in male testes – the testicular microbiome – may provide clues towards understanding a common form of male infertility.

Dr Massimo Alfano at the IRCCS Hospital San Raffaele in Milan, Italy, and his team have overturned the established idea that the testes are entirely free of bacteria using new technologies. 'These findings are actually surprising, because almost all medical textbooks mention that [the] human testes… is a microbiologically sterile microenvironment,' said Dr Alfano. 'For the first time ever, we [have] been able to quantify the bacterial DNA in the testes.'

Their results may have implications for men with azoospermia. This condition, in which a man's semen contains no sperm, affects 1 percent of all men, and 15 percent of infertile men. Of the few treatment options available, surgery is the most common. Testicular tissue is surgically removed from which sperm – in some cases, can be collected. In general, male infertility is associated with a higher risk of developing tumours and age-related diseases.

The results could lead to the development of future therapies for azoospermic men, as well as helping to identify patients for whom the surgical treatment would be ineffective, saving them from an invasive procedure.

Bacterial microbiomes have been shown elsewhere in the body to play a key role in maintaining the proper functioning of organs and tissue.

In this study the bacteria found in the testicular tissue of three groups of men were investigated; a group of fertile men, a group of men with azoospermia for whom surgical treatment was effective and a group for whom it was ineffective.

The bacterial microbiome of fertile men was found to be the most diverse with four main types of bacteria present. These bacteria are also present in the gut microbiome although in different relative numbers.

The men with azoospermia for whom treatment was effective had more bacteria present in their testicular microbiome but there was less diversity, with only two main types of bacteria found. While the men for whom surgery was ineffective had only one main type of bacteria. Entirely missing from these men was a particular type of bacteria that they found to be associated with sperm motility. This bacteria could be used as a clinical marker to identify men from whom sperm cannot be surgically retrieved, they suggest.

Specimens from only 15 men were investigated in the study published in Human Reproduction. More research is required to validate these findings. The most pressing question in the future will be whether restoring a normal testicular microbiome could restore sperm production in men with azoospermia.

The researchers also noted that the differences in the microbiome of azoospermic men compared with fertile men were similar to the differences seen in the gut microbiome between young and old individuals, indicating a further link between biological events related to ageing and infertility.